This application is a continuation-in-part of U.S. Ser. No. 346,423 filed on Feb. 5, 1982, and entitled Protective Overcoatings for Photoresponsive Devices. The disclosure of this application is totally incorporated herein by reference.
This invention is generally directed to an electrostatographic imaging member or device, containing certain silicone-silica hybrid crosslinked polymers; and more specifically, the present invention is directed to inorganic and organic photoresponsive devices with silicone-silica hybrid overcoatings. These overcoatings function primarily as a physical and chemical protectant for the photoresponsive member, and further allow the achievement of excellent release and transfer of toner images from such members. Also, the imaging member comprised of silicone-silica hydrid overcoatings of certain critical thicknesses possess acceptable residual voltages.
The formation and development of images utilizing photoresponsive devices is well known, one of the most widely used processes being xerography. In these processes the electrostatic latent image is developed by applying toner particles thereto, and subsequently the developed image is transferred to a permanent substrate such as paper. Development can be accomplished by a number of various known techniques including cascade development, powder cloud development, magnetic brush development, liquid development, and the like.
Recently there has been disclosed for use in xerographic imaging systems, inclusive of those with a double charging process, overcoated layered inorganic and organic imaging members. One of these members comprises a substrate, a hole injecting layer overcoated with a hole transport layer, and a photogenerating layer, followed by an insulating organic resin top coating. These devices have been found to be very useful in various imaging systems, and have the advantage that high quality images are obtained, with the overcoating acting primarily as a protectant. The details of this type of overcoated photoreceptor device is fully described in U.S. Pat. No. 4,251,612, on Dielectric Overcoated Photoresponsive Imaging Member and Imaging Method, the disclosure of which is totally incorporated herein by reference.
In one preferred method of operation as described in the aforementioned patent, the layered photoresponsive member is charged a first time with electrostatic charges of negative charge polarity, subsequently charged a second time with electrostatic charges of a positive polarity for the purpose of substantially neutralizing the charges residing on the electrically insulating surface of the member, followed by exposing the member to an imagewise pattern of activating electromagnetic radiation thereby forming a visible image, which is transferred to a receiving member. The photoresponsive device may subsequently be reused to form additional reproductions after erasure and cleaning have been accomplished.
There are also disclosed in the prior art various imaging devices with polysiloxane compounds. For example, U.S. Pat. No. 4,181,772 discloses an overcoated photoreceptor device, with an adhesive generating layer comprised of a photogenerating pigment dispersed in a copolymer of a siloxane and a dihydroxy compound, the copolymer being of the formula as illustrated in column 2, beginning at around line 60. This layer thus functions as a photogenerator, and as an adhesive in organic photoresponsive devices, thereby eliminating the need for additional adhesive layers while simultaneously allowing excellent generation of positive charges. Also, there is described in U.S. Pat. No. 3,861,915 solvent soluble block copolyesters of polysiloxanes of the type as illustrated in column 3, beginning at line 20. It is indicated in this patent that such block copolymers have excellent leveling and release properties, and can be used as additives in electrophotographic compositions for single layer planographic printing plates, which may be utilized directly without the necessity of a fountain solution, and which eliminate the problem of migration of sensitizing dyes in photoconductors. There is further disclosed in thhis patent that the novel copolyester polysiloxane copolymers are useful in single layer reusable electrophotographic films with improved surface characteristics, including the prevention of excessive wear.
Furthermore, disclosed in U.S. Pat. No. 4,009,032 are improved waterless lithographic plates, which are comprised of a copolymer of siloxane blocks crosslinked to an elastomeric ink releasing condition and organic thermoplastic blocks which are ink accepting. More specifically, there is disclosed in this patent that a master comprising a conventional substrate and an overlying layer of a copolymer having siloxane blocks crosslinked to an ink releasing elastomeric condition, and ink accepting organic thermoplastic blocks can be imaged with particulate imaging material, by softening the thermoplastic blocks, followed by hardening to bond the particular imaging material thereto. Thus, according to the teachings of this patent, the thermoplastic blocks permit the imaging material to be physically bonded thereto, and the siloxane blocks provide an insoluble ink releasing background area in order that no dampening or fountain solution is required. Similar teachings are present in U.S. Pat. Nos. 3,886,865; 3,865,588; and 3,775,115.
There is also disclosed in U.S. Pat. No. 4,371,600 release photoresponsive members with overcoatings comprised of certain crosslinked siloxy coupled dihydroxy compounds, such as bis-phenol-A copolymers. More specifically, there is described in this patent certain crosslinked siloxy coupled dihydroxy copolymers, having a molecular weight of from about 2,000 to about 250,000, and preferably from about 40,000 to about 100,000. These materials allow rapid release and transfer of toner particles from photoresponsive members to a permanent substrate.
Other prior art includes U.S. Pat. No. 4,277,287, which discloses silicone resin protective coatings for polycarbonates, metal substrates, glass, wood and the like, reference the teaching in column 6, beginning at line 4; U.S. Pat. No. 3,434,832 which describes a photoconductive member with a protective coating of a film forming resin and at least one metallic stearate; U.S. Pat. No. 2,901,349; and Japanese Publication No. 011734 of September 1978 to Toray Industries, Inc.
When selecting certain organic or inorganic photoresponsive members for different imaging systems, various problems, which are detrimental to the performance and the life of the photoreceptor from both a physical and chemical contamination standpoint can be encountered. Thus, for example, organic amines, mercury vapor, or human fingerprints can cause crystallization of amorphous selenium photoreceptors resulting in undesirable copy quality and copy deletion. In addition, physical problems such as scratches on both organic and inorganic photoresponsive devices can cause unwanted printout on the final copy. Furthermore, organic photoresponsive devices sensitive to oxidation, and subjected to electric charging devices can suffer reduced useful life in a machine environment. Also, with certain overcoated organic photoreceptors, various problems have been encountered with regard to the development and transfer of the images involved. Thus, for example, the toner materials used for development do not release sufficiently from the photoresponsive surface leaving unwanted toner particles thereon causing such particles to be subsequently embedded into, or transferred from the imaging surface in later imaging steps resulting in undesirable images of low quality and/or high background. In some instances the dry toner particles also adhere to the imaging member in print background areas due to the adhesive attraction of the toner particles to the photoreceptor surface. This can be particularly troublesome when most silicone elastomeric polymers or resins are employed as photoreceptor overcoating materials for their toner release characteristics. Therefore, low molecular weight silicone components can migrate to the surface of the polymer layer and act as an adhesive toward dry toner particles brought in contact therewith during the image development step. There thus results undesirable high background prints since the toner particles, along with the toner image, are efficiently transferred to the receiving sheet when, for example, simultaneous transfer and fixing is thermally accomplished. The imaging members of the present invention eliminate many of these prior art problems.